The present invention relates to a method for friction stir welding stacked surfaces.
Friction stir welding is a method for joining members in which a round shaft (called a rotary tool) is rotated and inserted into a joint portion between the members, and the rotating tool is moved along the joint line, thereby heating, mobilizing and plasticising the material in the joint portion in order to perform solid-phase welding of the members. The rotary tool comprises a large-diameter portion and a small-diameter portion. The small-diameter portion is inserted into the joint between the members to be welded to an extent that the end surface of the large-diameter portion contacts the members. The small-diameter portion is provided with a screw thread on its outer surface.
Moreover, a raised portion is formed on the side of the members in the joint region where the rotary tool is to be inserted, so that the metal material that forms the raised portion forms a supply of material to fill the gap between the two members. The large-diameter portion of the rotary tool is dimensioned to accommodate the raised portion.
These features are disclosed in Japanese Patent Laid-Open Publication No. 11-90655 (U.S. Pat. No.6050474).
Friction stir welding can be employed for joining stacked (superposed) surfaces. When the stacked members are to be joined through friction stir welding, a notch is formed on the stacked surfaces. An example is shown in FIG. 4 (A), which is a vertical cross-sectional view showing the members during friction stir welding, and in FIG. 4 (B), which is a vertical cross-sectional view showing the state of the welded joint after the friction stir welding. FIG. 4 (B) is a simplified explanatory view. The friction stir welding is performed by inserting a rotary tool 50 into the stacked members from the upper direction. The stirred region shown by the hatching and the stacked surface of the two members constitute a notch B knuckled to the upper side.
An object of the present invention is to provide a friction stir welding method which is capable of preventing the generation of notches at the stacked surfaces.
The present invention calls for stacking a first member and a second member, providing a groove on the stacked surface of the first member extending along the intended direction of the friction stir welding, and performing friction stir welding of the stacked surfaces along the groove using a rotary tool having a small-diameter portion with a diameter greater than the width of the groove.